Oxygen balance

The oxygen balance, short ( engl. oxygen balance ) of any material mixture gives the relative amount of oxygen, which is excessive or absent ( with a negative sign) in order to achieve a balance between oxidants and combustible components. A substance mixture with a balanced oxygen balance may be reacted by heating in a sealed container, without external supply of oxygen to completely oxidised products are thus completely burnt without oxidant remains.


Is the number of atoms of chemical element in a chemical compound with the formula, and is the molar mass of the compound. The mixture of substances with the total mass consists of various chemical compounds (components) with the masses and the mass fractions. The number of moles of the element in the mixture is then calculated as:

Be the most stable under combustion conditions valence of the chemical element.

The lack or excess for a complete valences in valence mole results from a sum of all chemical elements.

The oxygen balance is calculated from:


Here, g / mol.

List of the most stable values ​​of all chemical elements under " combustion conditions ":

Calculation of the oxygen balance of the components

The oxygen balance of a substance mixture obtained after oxygen from the balance sheets of the individual components ( pure substances ) and their mass fractions:


Digester gas -air mixture

Fermentation gas is a combustible mixture of about 40 % by weight of CH4 (methane), and 60 wt % CO2 ( carbon dioxide), which is formed during the bacterial decomposition of organic materials (for example, in the human gut ). Air is a mixture of 75.5 wt % N2 ( nitrogen), 23.1 wt % O2 (oxygen), 1.3 wt % Ar (argon ) and 0.1 wt % CO2 ( carbon dioxide) in addition to negligible trace levels of other noble gases, hydrocarbons, hydrogen, nitrogen oxides, carbon monoxide, ozone and dust.

Which oxygen balance, a mixture of 1 kg of digestion gas, and kg air, when viewed as a variable?

The following applies:

For the number of moles of the elements contained yields:

For the oxygen balance as a function of the result is:

For is. With the standard density (15 ° C) and it follows that:

Air-fuel ratio when air-fuel mixtures

In heating systems, and internal combustion engines burning or fuels are burned with oxygen in the air and used the thus liberated energy for heating or for the performance of mechanical work. Crucial for the best possible utilization of the stored chemical energy in the fuel is a suitable ratio of combustion air and fuel. The amount of air that is at least required for a complete combustion per Massenseinheit fuel is referred to as a minimum air demand. The ratio of the actually supplied to the theoretically required for complete combustion minimum amount of air is called air ratio and usually labeled. In an ideal combustion with stoichiometric air ratio is so. Fuel-air mixtures contain denotes an excess of fuel and be as rich mixture, while those included with an excess of air, and are called lean mixture.

See also:

  • Lambda probe
  • Calorific value
  • Excess air coefficient
  • Combustion
  • Measure of process engineering
  • Chemical size